Tuning of PID controllers based on sensitivity margin specification

This paper presents an alternative method to the one proposed by Astrom and Hagglund (1995) for the tuning of PID controllers with specification of sensitivity margin M/sub s/. The method is based on the following steps: 1) to delimit the range of frequencies in which it is possible to contact with a specific point of a circle of radius M/sub s//sup -1/ centered at -1; 2) to explore the frequencies where this contact takes place tangentially, because these frequencies will only be possible solutions; and 3) to choose one of the possible solutions. Some examples have been selected in order to show the main features of the proposed method.